Anion receptor compounds for non-aqueous electrolytes

ABSTRACT

A new family of aza-ether based compounds including linear, multi-branched and aza-crown ethers is provided. When added to non-aqueous battery electrolytes, the new family of aza-ether based compounds acts as neutral receptors to complex the anion moiety of the electrolyte salt thereby increasing the conductivity and the transference number of LI +   ion in alkali metal batteries.

This invention was made with Government support under contract numberDE-AC02-76CH00016, between the U.S. Department of Energy and AssociatedUniversities, Inc. The Government has certain rights in the invention.

This is a divisional of application Ser. No. 08/862,734, filed May 23,1997, now U.S. Pat. No. 5,789,585, issued Aug. 4, 1998, which in turn isa divisional of application of Ser. No. 08/492,201, filed Jun. 19, 1995and now U.S. Pat. No. 5,705,689 issued Jan. 6, 1998.

BACKGROUND OF THE INVENTION

This invention relates to the design, synthesis, and application of anew family of aza-ether based compounds which act as anion receptors innon-aqueous battery electrolytes. As a result, the anion receptors ofthe present invention can be used as additives to enhance the ionicconductivity and cation transference number of non-aqueous batteryelectrolytes. More specifically, the new family of aza-ether basedcompounds includes substituted linear aza-ethers, multi-branchedaza-ethers, and aza-crown ethers wherein the hydrogens on the N aresubstituted with an R group. R is an electron withdrawing group such asCF₃ SO₂, CF₃ CO, CN, or SO₂ CN. The electron deficient N centers cancomplex anions very effectively.

Considerable research has been conducted on the design and synthesis ofreceptor molecules for the selective complexation of ions. Whilecompounds which serve as cation receptors have been studied widely,information on host molecules for anions has been scarce. For example,U.S. Pat. No. 5,130,211 to Wilkinson, et al. describes anelectrochemical cell which has an electrolyte solution containing anorganic solvent, an alkali metal salt and at least one sequesteringagent. The sequestering agent described by Wilkinson, et al., can be aglyme, crown ether or cryptand. The sequestering agents disclosed byWilkinson, et al. are useful in complexing with the alkali moiety of theelectrolyte salt and thus, act as cation complexing agents.

Dietrich (B. Dietrich, J. Pure and Appl. Chem. 65, 1457 (1993)) hasreviewed the field of anion receptors and has pointed out that therequirements for anion receptors are different than those for cationreceptors. This is because of the larger size of the anions and the widevariety of shapes encountered in polyatomic anions. At present, twocategories of anion receptors have been developed. One includes hostmolecules that contain positively charged sites, the others areneutrally charged anion receptors. For the first category, thepositively charged sites such as ammonium or guanidinium binding sitesact as large cations and can only be used in aqueous solutions where theanions are already dissociated. These types of anion receptors cannot beused in non-aqueous electrolytes to increase ion dissociation. In thesecond category, the anion binding depends on either hydrogen bonding orelectron deficient Lewis acid metal centers (Sn, Hg, B, or Si) inorganic structures. Although these neutral receptors are useful asselective anion binding sites in both aqueous and non-aqueous solutions,they are not suitable for use in aprotic non-aqueous electrolytes.Receptors which utilize hydrogen bonding will react with lithium orsodium and will thus degrade both the anode and the electrolyte. TheLewis acid type receptors often contain heavy metals and as a resulttailoring of a structure to fit various anions is difficult.Furthermore, their electrochemical stability is unknown and the releasedmetals from decomposition would be deleterious in a battery electrolyte.The anion receptors of the present invention are a new type of neutralreceptors. The novel feature of these receptors is that the anionbinding is accomplished neither through a metal Lewis acid center northrough hydrogen bonding, but through an electron deficient center at Natoms that is induced by the substitution of the amine hydrogens withelectron withdrawing groups. The receptors are electrochemically stableand can be easily designed to fit various anion sizes and shapes. Theirchemistry is compatible with that of electrodes, salts, and solventscommonly used in non-aqueous battery electrolytes.

Moreover, in the past, inorganic, cost effective salts such as LiCl andLiBr have not been used as electrolyte salts because of their lowsolubility and conductivity. LiI has been used as an electrolyte to someextent because LiI has higher conductivity than LiCl and LiBr. However,I⁻ is oxidized above 2.5 volts vs. Li so it could only be used in lowvoltage primary batteries such as Li/FeS₂.

Accordingly, there is still a need in the art of alkali metal batteriesand especially lithium batteries for electrolyte additives which cancomplex anions, yet are stable in alkali metal and especially lithiumbatteries. There is also a need in the art of alkali metal batteries toenhance the conductivity of inexpensive and environmentally friendlyinorganic salts such as LiCl, LiBr and LiI. In addition, there is a needto increase the transference number of the Li⁺ ion. In many non-aqueouselectrolytes, in particular polymer electrolytes, the transferencenumber of the Li⁺ ion is low. This introduces additional polarizationlosses in batteries and reduces the utilization of the cathode material.

It is therefore, an object of the present invention to provide a newfamily of compounds which enhances the conductivity of alkali metalbattery electrolytes by complexing with the anion moiety of theelectrolyte salt and also by increasing the transference number of theLi⁺ ion.

Another object of the present invention is to increase the conductivityof cost effective electrolyte salts such as LiCl, LiBr and LiI.

Another object of the present invention is to provide improvedelectrochemical cells by use of electrolyte additives.

SUMMARY OF THE PRESENT INVENTION

The present invention, which addresses the needs of the prior art,provides a new family of aza-ether based compounds which act as anionreceptors in non-aqueous battery electrolytes. When added to non-aqueouselectrolytes, the neutral receptors of the present invention complex theanion moiety of the electrolyte salt, thereby increasing theconductivity of and the transference number of Li⁺ ion in alkali metalbatteries. The present invention also provides methods of makingelectrochemical cells including aza-ether anion receptors as electrolyteadditives for both primary and secondary batteries. Electrolyte solventsuseful for the electrochemical cells of the present invention includeorganic solvents such as tetrahydrofuran, polymer and gel electrolytesincluding a solution of lithium salt.

As a result of the present invention, stable anion receptor compoundsare provided which increase dramatically the conductivity ofelectrolytes for alkali metal and especially lithium batteries. Theelectrolyte conductivity is increased because the aza-ether basedcompounds of the present invention complex anion moieties, non-aqueouselectrolytes thereby increasing the concentration of alkali cationsavailable for transport. As a result of using the anion receptor of thepresent invention alkali metal batteries are provided which havesignificantly increased rate capability or discharge current density.The enhanced batteries of the present invention also have increasedcathode utilization because of the increased Li⁺ ion transferencenumber.

Moreover, when added to liquid, non-aqueous electrolytes containingsalts such as LiCl, LiBr or LiI, the aza-ether based compounds of thepresent invention provide a salting-in effect which results in increasedsolubility and electrolyte conductivity. Thus, another importantadvantage of using the aza-ether based compounds of the presentinvention is the significant cost savings resulting from using low costelectrolyte salts such as LiCl, LiBr and LiI.

Other improvements which the present invention provides over the priorart will be identified as a result of the following description whichsets forth the preferred embodiments of the present invention. Thedescription is not in any way intended to limit the scope of the presentinvention, but rather only to provide a working example of the presentpreferred embodiments. The scope of the present invention will bepointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates near edge X-ray absorption fine structure spectra(NEXAFS) at the K edge of chlorine for (a) LiCl salt, (b) 0.2M LiCl/THFsolution, (c) 0.2M LiCl+0.2M L6H in THF solution, and (d) 0.2M LiCl and0.2M L6R in THF solution.

FIG. 2 illustrates NEXAFS spectra at the K edge of chlorine of solidstate samples for: (a) 0.2M LiCl+0.2M L4R, (b) 0.2M LiCl+0.2M L5R, (c)0.2M LiCl+0.2M L6R, and (d) 0.2M LiCl+0.2M L8R.

FIG. 3 illustrates NEXAFS spectra at the K edge of bromine for (a) 0.2MLiBr in THF solution, (b) 0.2M LiBr+0.2M L2R in THF solution, (c) 0.2MLiBr+L4R in THF solution, (d) 0.2M LiBr+L6R in THF solution.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a new family of anion receptors andmethods for their preparation. As used in the present invention, anionreceptor means a compound which binds anions thereby moving theionization equilibrium point of electrolyte salts towards increasing theavailability of cation moieties.

The present invention also provides methods of use of these newcompounds to enhance the ionic conductivity of alkali salts innon-aqueous electrolyte solutions. More specifically, the presentinvention provides linear aza-ethers, multi-branched aza-ethers andcyclic aza-crown ethers.

The linear aza-ethers of the present invention include compounds of theformula ##STR1## wherein n₁ =0-20, n₂ =0-20, m=0-20 and n₁ =n₂ >0 and Ris an electron withdrawing group such as CF₃ SO₂, CF₃ CO, CN or SO₂ CN.

Linear aza-ethers of the present invention also include compounds of theformula ##STR2## wherein n>60 and R is a substituent selected from thegroup consisting of CF₃ SO₂, CF₃ CO, CN and SO₂ CN.

The multi-branched aza-ethers of the present invention include compoundsof the formula NR'₃, CR"₄, wherein R' is R₂ --N--CH₂ --CH₂, R" is R₂NCH₂ CH₂ NRCH₂ --, and R is a substituent selected from the groupconsisting of CF₃ SO₂, CF₃ CO, CN and SO₂ CN.

Examples of Multibranched aza--ethers are Set Forth Below. ##STR3##wherein R is again an electron withdrawing groups used to substituteamine hydrogen atoms, the group including CF₃ SO₂, CF₃ CO, CN or SO₂ CN.

The cyclic aza crown ethers of the present invention include compoundsof the formula ##STR4## Each N has an R group thereon and R is anelectron withdrawing group such as CF₃ SO₂, CF₃ CO, CN or SO₂ CN.

It has been unexpectedly discovered that when the substituted aza-etherbased compounds of the present invention are added to electrolytesutilized in either primary or secondary alkali metal batteries, theionic conductivity is dramatically increased. Near Edge X-ray AbsorptionFine Structure (NEXAFS) spectroscopy studies have shown that anions ofalkali salts and especially lithium salts found in many electrolytes arecomplexed with the nitrogen groups bearing electron withdrawing groups.

Without being bound by any theory, it is believed that the aza-etherbased compounds of the present invention increase electrolyteconductivity because they complex the anion moieties of electrolytesalts. Anion complexation causes an increase in the concentration andtransference number of cation moieties thereby increasing the ratecapability and cathode utilization of an electrochemical cell.Additionally, when used with lithium chloride, lithium bromide orlithium iodide, a salting-in effect takes place which increases thesolubility of these salts. "Salting in" refers to the mutual increase inthe solubilities of an electrolyte and an organic compound added to thesame solvent. As a result of anion complexation properties, the newfamily of aza-ether based compounds of the present invention can be usedas electrolyte additives in both primary and secondary batteries.

In a primary cell of the present invention other cell components includean anode composed of lithium or another alkali metal, a cathode composedof SO₂, CuO, CuS, Ag₂ CrO₄, I₂, PbI₂, PbS, SOCl₂, V₂ O₅, MoO₃ or MnO₂ orpoly(carbon monofluoride) (CF)n. Because of the high solubility oflithium in aqueous solutions, non-aqueous solvents are used aselectrolyte solvents. Organic solvents, such as acetonitrile andpropylene carbonate and inorganic solvents, such as thionyl chloride aretypical. A compatible solute such as LiI, LiBr or LiCl is added toprovide the necessary electrolyte conductivity.

Organic anion lithium salts can also be used as solutes to provideelectrolyte conductivity. Examples of organic anion salts include LiSO₃CF₃, LiN(SO₂ CF₃)₂ and LiC(SO₂ CF₃)₃. Other examples of organic anionsalts are lithium salts with fluorinated sulfonate aromatic anions.

The aza compounds of the present invention are also effectiveelectrolyte additives for secondary or rechargeable batteries. Thesecondary electrochemical cell containing the electrolyte additive ofthe present invention includes an alkali metal anode or an anodecontaining a material capable of reversibly incorporating an alkalimetal, a cathode capable of reversibly incorporating an alkali metal, analkali metal incorporated in at least one of said anode and cathode andan electrolyte. The electrolyte includes an organic solvent, a salt ofthe alkali-metal found in either the anode or cathode and an electrolyteadditive which is an anion complexing agent and can complex with theanion moiety of the electrolyte salt.

The anode material useful for the rechargeable battery of the presentinvention includes lithium, lithium alloys, such as Li--Al, Li--Si,Li--Cd, lithium-carbon or lithium-graphite intercalation compounds,lithium metal oxide intercalation compounds such as Li_(x) WO₂ or LiMoO₂or a sulfide such as LiTiS₂. The anode can also be made from sodiummetal or a sodium alloy such as sodium-lead.

Suitable cathode materials include transition metal oxides, metalhalides or chalcogenides which intercalate lithium. Chalcogens areunderstood by those of ordinary skill in the art to include thechemically-related elements from Group VI of the periodic table, namelysulfur, selenium, tellurium and polonium. Preferred transitionmetals-include manganese, nickel, iron, chromium, titanium, vanadium,molybdenum and cobalt. Preferred compositions include molybdenumsulfides, vanadium oxides and manganese oxides. MoS₂, V₆ O₁₃, Mo₆ S₈ andMnO₂ are more preferred, and MnO₂ is most preferred.

Other cathode materials useful for the electrochemical cell of thepresent invention include poly(carbon disulfide) polymers,organo-disulfide redox polymers, polyamine andorgano-disulfide/polyaniline composites. Examples of oxides andchalcogenides useful in the present invention include: Li₂.5 V₆ O₁₃,Li₁.2 V₂ O₅, LiCoO₂, LiNiO₂, LiMn₂ O₂, LiMnO₂, Li₃ NbSe₃, LiTiS₂,LiMoS₂. Organo disulfide redox polymers are based on the reversibleelectrochemical dimerization/scission orpolymerization/de-polymerization of organo disulfide polymers by thereaction:

    --(S--R--S)--.sub.n +2ne.sup.- =nS.sup.- --R--S.sup.-

where R is an aliphatic or aromatic moiety and n>50. An example is 2,5dimercapto-1,3,4-thiadiazole.

Cathode materials useful for sodium batteries include oxides of Ti, V,Cr, Mn, Co, Ni, Mo and sulfides of Mo, Ti and Ta. Poly(carbon disulfide)or other organo-disulfide polymers such as 2,5 dimercapto-1,3,4thiadiazole are also suitable cathode materials for the electrochemicalcells of the present invention.

It is desirable that the cathode maintain its electrical conductivity atall states of charge. Conductivity can be enhanced by adding anelectrically-conductive chemically-inert material, such as acarbonaceous material like graphite or carbon black, to the cathode.

In assembling the cells of the present invention, the cathode istypically fabricated by depositing a slurry of the cathode material, theelectrically conductive inert material, the binder and a fugitive liquidcarrier such as cyclohexane, on the cathode-current collector, and thenevaporating the carrier to leave a coherent mass in electrical contactwith the current collector.

The anode can be fabricated from highly graphitic carbonaceous materialin particulate form with a suitable inert polymeric binder at a level ofabout 2% by weight or less of polymer to anode material. Expansion andcontraction of the anode during cell cycling can cause the carbonaceousparticles to lose electrically conductive contact with one another.Conductivity can be similarly enhanced by adding anelectrically-conductive material, such as carbon black, to the anodematerial.

In assembling the cell of the present invention, the anode can similarlybe fabricated by depositing a slurry of the highly graphiticcarbonaceous anode material, the electrically-conductive inert material,the binder and a fugitive liquid carrier such as hexane on theelectrically-conductive anode support and then evaporating the carrierto leave a coherent mass in electrical contact with the support.

The cathode assembly is then combined with the anode assembly with theporous polymeric electrode separator sandwiched therebetween. Thepreferred way of constructing high voltage rechargeable cells is to makethem by using the cathode material in the discharged state which cathodematerial is lithiated metal oxides, materials stable in air.Alternatively, if the cathode-active material is non-lithiated orinsufficiently lithiated, then lithium either as lithium metal, alloyedlithium or intercalated lithium is incorporated in the anode in anamount that is at least sufficient to discharge the cathode material.The layered assembly is then wound around the metallic center post toform a spiral assembly which is then placed into the cell container towhich is added the electrolyte solution into which the additive of thepresent invention has been dissolved. The cell container is then coveredwith a cell cap.

The electrolyte solution includes an electrolyte salt of the alkalimetal exchanged between the cathode and anode dissolved in theelectrolyte solvent. The electrolyte salt should be compatible with boththe cathode-active material, the anode material and the aza-ether basedadditives of the present invention. When the alkali metal is lithium,suitable lithium electrolyte salts include LiAsF₆, LiPF₆, LiClO₄, LiBF₄,LiSbF₆, LiB(C₆ H₅)₄, LiCF₃ SO₃, LiN(CF₃ SO₂)₂, LiSO₃ F, LiAlCl₄, LiBr,LiCl, LiI and mixtures thereof. LiAsF₆, LiCF₃ SO₃, LiN(CF₃ SO₂)₂ andmixtures thereof are preferred.

Suitable electrolyte solvents include non-aqueous, liquid polar solventssuch as ethylene carbonate, dimethyl carbonate and mixtures thereof.Other useful solvents are cyclic and acyclic ethers, organic carbonates,lactones, formates, esters, sulfones, nitrites and oxazolidinones.Useful electrolyte solvents include tetrahydrofuran; 2-methyl furan;4-methyldioxolane; 1,3-dioxolane; dimethoxyethane; dimethoxymethane;ethylene carbonate; propylene carbonate; γ-butyrolactone; methylformate; sulfolane; acetonitrile; 3-methyl-2-oxazolidinone and mixturesthereof. Polymer electrolytes of several types are also useful forelectrochemical cells of the present invention. One type consists oflithium salts dissolved in linear polyethers such as poly(ethyleneoxide). Because it is important that the polymer be amorphous and have alow glass transition temperature, the polymer electrolytes may bedesigned as polymer networks, branched or comb shaped polymers whichhave flexible inorganic backbones such as (P=N--)_(n) or (--SiO--)_(n).A polymer electrolyte may be further modified by addition ofplasticizers such as organic carbonates.

Gelled electrolytes are another type of electrolytes that are useful forthe electrochemical cells of the present invention. Gelled electrolytesinclude a solution of lithium salt in a liquid organic solvent and asupporting matrix of a polymer such as poly(acrylo nitrile) orpoly(vinylidene fluoride). Examples of lithium salts which can be usedin gelled electrolytes are LiCF₃ SO₃, LiN(CF₃ SO₂)₂, LiCl, LiBr. Binarysolvents such as mixture of ethylene carbonate and propylene carbonatecan also be used as liquid solvents in gelled electrolytes.

Often blends of these solvents are used to enhance the conductivity. Inaddition the solvent can contain various additives. Examples are cyclicethers and CO₂ to improve the cyclability of the lithium electrode, andvarious additives to prevent migration of sulfur from TiS₂ cathodes tothe anode. Additives are also often added for overcharge protection andhigh temperature storage.

In a secondary electrochemical cell, the aza-compounds of the presentinvention complex the anion moieties found in the electrolyte therebyincreasing the availability of the free cations. For example, in alithium or lithium ion battery, upon leaving the anode, the lithiumcation is shuttled across the electrolyte for incorporation into thehost lattice of the cathode. Thus, by complexing the anion moiety, morepositively charged lithium ions become available for transfer therebyincreasing dramatically the ionic conductivity of the electrochemicalcell.

The focus of the examples set forth below has been to provide novelsyntheses for the aza compounds of the present invention. It has beenunexpectedly found that by reacting an unsubstituted aza-ether with ananhydride bearing an electron withdrawing group under conditionspromoting the substitution of amine hydrogens, a new family ofsubstituted aza-ether compounds was provided. Conditions known topromote the substitution of amine hydrogen included keeping the reactionvessel under a nitrogen purge at atmospheric pressure and in a coolingbath at about -20° C. over a period of time from about 2.5 hours toabout 19 hours.

NEXAFS spectroscopy studies have been conducted illustrating theefficacy of the aza family of compounds of the present invention aselectrolyte additives which increase conductivity of electrolytes usedin alkali electrochemical cells.

EXAMPLE

The Examples set forth below also serve to provide further appreciationof the invention but are not meant in any way to restrict the effectivescope of the invention.

Example 1 Preparation ofN,N,N',N',3,6-Hexa(trifluoromethylsulfonyl)-3,6-diazaoctane-1,8-diamine

In this example, a linear aza anion complexing agent of the formula##STR5## was prepared.

40.6 g of trifluoromethane sulfonic anhydride in 30 ml of anhydrouschloroform was added to a solution of 2.92 g of triethylenetetramine and14.5 g of triethylamine in 100 ml of chloroform, and kept under nitrogenin a cooling bath at -20° C. over a period of 2.5 hours. After stirringthe mixture for 0.5 hours, the cooling bath was removed and the mixturewas stirred at room temperature for 1 hour until a white precipitateformed. 11.3 g of the white precipitate was collected and washed withchloroform. After washing and drying, the chloroform filtrate wasevaporated to dryness. Methanol was added to the residue and the mixturewas left to stand overnight. An additional 3.9 g of precipitate wascollected and combined with the crude product. The combined product wasdissolved in a small amount of acetone and filtered. Methanol was slowlyadded to the filtrate until a crystalline product was isolated. Themixture was filtered to yield 14.2 g. of the pure product. The producthad the following identification characteristics for melting point,hydrogen NMR shifts and IR absorption bands: m.p. 134-5° C.; NMR(Acetone d₆), δ 4 (m, 8H), 4.5 (m, 4H), ppm; IR (KBr) 3043.7, 2998.4,2971.7, 1457.4, 1393.3, 1202.7, 1122.3, 1009.3, 858.5, 774.1, 731.5cm⁻⁻¹.

Example 2 Preparation ofN,N,N',N',3,6-Hexa(trifluoroacetyl)-3,6-diazaoctane-1,8-diamine

In this example, another linear aza anion complexing agent was prepared.This complexing agent has the formula of ##STR6##

2.19 g of triethylenetetramine in 80 ml of anhydrous chloroform wasreacted at room temperature with 22.7 g of trifluoroacetic anhydride inthe presence of 11.1 g of triethylamine over a period of 19 hours. Theresulting white crystalline product was collected by filtration andwashed with chloroform. The crude product was recrystallized from anacetone-chloroform mixture to yield 6.3 g of the pure product. Theproduct had the following characteristics for melting point, hydrogenNMR shifts and IR absorption bands: m.p. 132-4° C.; NMR (Acetone d₆), δ3.8 (m, 8H), 4.3 (m, 4HO, ppm; IR (KBr), 2951.6, 1755.1, 1689.5, 1549,1458.9, 1367.8, 1329.7, 1290.9, 1170.7, 1061.9, 1020.7, 921, 867.2, 751,711.4, 634.3, 526.4 cm⁻¹.

The compounds in Examples 1 and 2 above are linear aza-anion complexingagents. It has been found that when used as electrolyte additives withLiCl, LiBr and LiI salts in THF as the solvent, the chain lengthrequired for anion complexation is a function of the anion size. Thus, alinear aza-compound with two nitrogens was sufficient to complexchloride ions, a linear aza-compound with three nitrogens was requiredto complex bromide anions and a linear aza-compound containing fournitrogens was required to complex iodide anions.

Example 3 Preparation of1,4,8,11-Tetra(trifluoromethylsulfonyl)-1,4,8,11-tetraazacyclotetradecane

In this example a cyclic aza crown compound of the formula ##STR7## wasprepared.

11.8 g of trifluoromethane sulfonic anhydride in 20 ml of chloroform wasadded to a solution of 1.4 g of 1,4,8, 11-tetraazacyclotetradecane in100 ml of anhydrous chloroform, and kept in a cooling bath at -20° C.under nitrogen over a period of 50 minutes. After completing theaddition, the cooling bath was removed and the mixture was stirred atroom temperature for 1.5 hours. 4.3 g of precipitate was collected andwashed with chloroform. The chloroform filtrate was then washed withwater and dried over anhydrous magnesium sulfate to yield an additional0.47 g of crude product. The combined crude product was recrystallizedfrom acetone to yield 4.0 g of pure product. The product had thefollowing characteristics for melting point, hydrogen NMR shifts and IRabsorption bands: m.p. 226-7° C.; NMR (Acetone d₆), δ 2.4 (m, 4H), 3.8(m, 16H) ppm; IR (KBr) 2962.43, 2892.8, 1472.2, 1382.6, 1204.8, 1125.1,1047.5, 975.2, 789.7, and 750.7 cm⁻¹.

Example 4 Preparation of1,4,8,11-Tetra(trifluoroacetyl)-1,4,8,11-tetraazacyclotetradecane

Another cyclic aza-compound of the formula ##STR8## was prepared in thisexample.

1.2 g of 1,4,8,11-tetraazacyclotetradecane and 3.03 g of triethylaminein 100 ml of anhydrous chloroform was mixed with 6.3 g oftrofluoroacetic anhydride, and kept in a cooling bath at -20° C. undernitrogen over a period of 20 minutes. The flask was removed from thecooling bath and the reaction mixture was stirred at room temperaturefor 2 hours. The collected precipitate was recrystallized from anacetone chloroform mixture. The pure product yield was 3.3 g and had thefollowing characteristics for melting point, hydrogen NMR shifts and IRabsorption bands: m.p. 217-80° C.; NMR (Acetone d₆), δ 1.9-2.8 (m, 4H,3.5-4 (m, 16 H) ppm; IR (KBr) 2954.4, 2903.3, 1690.2, 1524.8, 1430.8,1372.5, 1151.9, 992.4, 865.5, 731.9 cm⁻¹.

The compounds synthesized in Examples 3 and 4 are crown aza-ethers basedcomplexing agents. When used as electrolyte additives for LiCl, LiBr andLiI salts in THF as the solvent, the crown size required forcomplexation varies.

Example 5 Conductivity Studies

In this example the ionic conductivity of electrolyte solutionscontaining various aza-ether compounds of the present invention wasmeasured and compared with the conductivity of electrolyte solutionwithout additives.

Home built conductivity cells having platinum electrodes were calibratedusing 0.05 N in a standard aqueous solution of potassium chloride.Conductivity measurements were made at 25° C. using a Hewlett-Packard4129 Impedance Analyzer in the frequency range from 5 Hz to 10 MHz. Theionic conductivity of solutions formed by adding various aza-ethercompounds to the 0.2M LiCl/THF solutions was compared with theconductivity of LiCl-THF solution without additives. The data issummarized in Table I below. The structures of the nomenclature used inTable I are summarized in Table II below.

                  TABLE I                                                         ______________________________________                                        Composition        Conductivity                                               (0.2M LiCl + 0.2M aza-ether)                                                                     (S · cm.sup.-1)                                   ______________________________________                                        LiCl               1.6 × 10.sup.-6                                      LiCl + L6H         4.2 × 10.sup.-6                                      LiCl + L4R         8.4 × 10.sup.-5                                      LiCl + L5R         1.4 × 10.sup.-4                                      LiCl + L6R         7.2 × 10.sup.-4                                      LiCl + L8R         1.4 × 10.sup.-3                                      LiCl + M6R         1.7 × 10.sup.-3                                      LiCl + C4R         2.3 × 10.sup.-4                                      ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Nomenclature   Structures                                                     ______________________________________                                        L6H            H(NHCH.sub.2 CH.sub.2).sub.3 NH.sub.2                          L4R            R(NRCH.sub.2 CH.sub.2)NR.sub.2                                 L5R            R(NRCH.sub.2 CH.sub.2).sub.2 NR.sub.2                          L6R            R(NRCH.sub.2 CH.sub.2).sub.3 NR.sub.2                          L8R            R(NRCH.sub.2 CH.sub.2).sub.5 NR.sub.2                          M6R            N(CH.sub.2 CH.sub.3 NR.sub.2).sub.3                            C4R            Cyclic (CH.sub.2 RNCH.sub.2 CH.sub.2 RNCH.sub.2).sub.2                        R = CF.sub.3 SO.sub.2.sup.-                                    ______________________________________                                    

The ionic conductivity data of Table I shows that when unsubstitutedaza-ether compounds were added to a LiCl/THF solution, the increase inionic conductivity was negligible. When aza compounds substituted withCF₃ SO₂ ⁻ were added to a LiCl/THF solution, the ionic conductivityincreased dramatically from about one to about three orders ofmagnitude.

It has also been found that the ionic conductivity depended on thenumber of R--N groups in the anion receptor additives. The ionicconductivity increased as the number of electron withdrawing groupsincreased, reaching a plateau when the number of electron withdrawinggroups was six. Since the R groups were strong electron withdrawinggroups, a positively charged environment surrounding the nitrogen atomswas created. The resulting anion complexation would create more free Li⁺ions, which in turn increased the ionic conductivity of the electrolyte.

Example 6 NEXAFS Studies

In order to confirm that the anions are complexed with nitrogen atoms inR-substituted aza-ether compounds and to find out the detailed structureof the formed complexes, NEXAFS studies on single crystals of theresulting complexes were conducted.

NEXAFS measurements were made at beam line X19A of the NationalsSynchrotron Light Source. The data were collected as fluorescenceexcitation spectra using a large solid angle ionization chamber as thefluorescence detector. After being used in conductivity measurements,the electrolyte solutions were poured into cells with Kapton windows forNEXAFS studies. Each of these solutions were then dropped on Kaptontapes to evaporate the THF solvent for studying anion complexation insolid state. The results for electrolyte solutions are shown in FIG. 1and the results for solids are shown in FIG. 2.

FIG. 1 shows x-ray absorption curves, at the chlorine K edge for (a)LiCl salt, (b) 0.2M LiCl/THF solution, (c) 0.2M LiCl+0.2M L6H in THFsolution, and (d) 0.2M LiCl+0.2 M L6R in THF solution. The "white line"peak above the edge was due to dipole-allowed transitions to finalstates of p symmetry. For most of the chloride salt in solid state, thewhite line was split into several peaks as a result of the removal ofthe degeneracy of the final p states due to the electric fieldsurrounding the Cl⁻ ions caused by the paired cations. However, thewhite line in curve (a) for LiCl in the solid state was a featurelessbroad peak. Similar structures were found for Cl⁻ in free ion state,such as KCl in dilute aqueous solution. In curve (b), the "white line"did not change much for the LiCl salt dissolved in THF indicating thatthe interaction between solvent and Cl⁻ was not strong enough to cause asplitting. In curve (c), when unsubstituted aza-ether was added into thesolution, the white line structure was about the same as in curve (a)and (b), implying no complexation between this compound and the Cl⁻anion. In curve (d), a clear split was observed when the R-substitutedaza-ether compound was added into the solution. The results shown incurve (d) constituted a strong evidence that Cl⁻ is complexed withnitrogen atoms of the R-substituted aza-ether compounds but not with thenitrogen atoms of the unsubstituted aza-ether compounds.

FIG. 2 shows the x-ray absorption curves at the chlorine K edge forsolid samples obtained by evaporating THF solvent from mixed LiCl andR-substituted aza-ether compound solutions. The solutions used were: (a)0.2M LiCl+0.2M L4R, (b) 0.2M LiCl+0.2M L5R, (c) 0.2M LiCl+0.2M L6R, and(d) 0.2M LiCl+0.2M L8R. The white line splitting depends on the numberof R groups in the R-substituted aza-ether compounds complexed with Cl⁻.It was interesting to note that the intensity of a sharp feature labeled(A) correlated with number of R groups in the added aza-ether compounds.Thus, it was noted that the higher the number of R groups the sharperthe (A) feature of the white line splitting. A similar correlationexisted between the ionic conductivity and the number of R groups asshown in Table I. Since all of these spectra were for samples in thesolid state rather than in solution, it was concluded that stablecomplexes were formed in both solution and in solid state.

FIG. 3 shows x-ray absorption curves at the bromine K edge for (a) 0.2MLiBr/THF solution, (b) 0.2M LiBr+0.2M L2R in THF solution, (c) 0.2MLiBr+0.2M L4R in THF solution, (d) 0.2M LiBr+0.2M L6R in THF solution.As was observed in the case of chloride complexation, the white linesplitting for bromide depends on the number of R groups in theR-substituted aza-ether compounds complexed with Br⁻. It was noted thatfor bromide containing electrolyte solutions changes in the white lineappeared only when the anion receptor compound had at least threesubstituted nitrogens as shown by curves (c) to (d) of FIG. 3. Thus, itwas found that the larger the anion, the longer the substitutedaza-ether compound required to achieve desired anion complexation.

Thus, while there have been described what are presently believed to bethe preferred embodiments of the present invention, those skilled in theart will appreciate that other and further modifications can be madewithout departing from the true scope of the invention, and it isintended to include all such modifications and changes as come withinthe scope of the claims as appended herein.

What is claimed is:
 1. An electrochemical cell which comprises a non-aqueous liquid electrolyte solvent and an electrolyte additive including an aza-ether based anion receptor compound.
 2. The electrochemical cell of claim 1, wherein said anion receptor compound is selected from the group consisting of a substituted linear aza-ether, a substituted multi-branch aza-ether, a substituted cyclic aza-crown ether and mixtures thereof.
 3. The electrochemical cell of claim 2, wherein said substituted linear aza-ether, said substituted multi-branch aza-ether or said substituted cyclic aza-crown ether, each contain at least one substituent on at least one amine nitrogen, said substituent selected from the group consisting of CF₃ SO₂, CF₃ CO, CN and SO₂ CN.
 4. The electrochemical cell of claim 1, wherein said electrolyte solvent is selected from the group consisting of tetrahydrofuran, 2-methyl furan, 4-methyldioxolane, 1,3-dioxolane, 1,2-dimethoxyethane, dimethoxymethane, ethylene carbonate, propylene carbonate, γ-butyrolactone, methyl formate, sulfolane, acetonitrile and 3-methyl-2-oxazolidinone, dimethyl carbonate and dimethyl ether.
 5. The electrochemical cell of claim 1, further comprising an electrolyte solute selected from the group consisting of LiClO₄, LiAsF₆, LiBF₄, LiPF₆ and LiSbF₆, LiCF₃ SO₃, LiN(CF₃ SO₂)₂, LiB(C₆ H₅)₄, LiSO₃ F, LiAlCl₄, LiC(SO₂ CF₃)₃ and mixtures thereof.
 6. The electrochemical cell of claim 1, further comprising an electrolyte solute selected from the group consisting of LiCl, LiBr and LiI and mixtures thereof.
 7. The electrochemical cell of claim 1, further comprising an anode selected from the group consisting of lithium or sodium metal, lithium or sodium alloys, lithium carbon intercalation compounds, lithium graphite intercalation compounds, lithium metal oxide intercalation compounds, and mixtures thereof.
 8. The electrochemical cell of claim 1, further comprising a cathode selected from the group consisting of a transition metal oxide, a transition metal chalcogenide, a poly(carbon disulfide) polymer, an organo-disulfide redox polymer, a polyaniline, an organo-disulfide/polyaniline composite, an oxychloride and a defect garnet.
 9. The electrochemical cell of claim 8, wherein said transition metal oxide is selected from the group consisting of Li₂.5 V₆ O₁₃, Li₁.2 V₂ O₅, LiCoO₂, LiNiO₂, LiMn₂ O₂, LiMnO₂, Na₂ V₂ O₅, and NaCoO₂.
 10. The electrochemical cell of claim 8, wherein said transition metal chalcogenide is selected from the group consisting of NaTaS₂, NaTiS₂, Na₄ Mo₆ S₈, Li₃ NbSe₃, LiTiS₂ and LiMoS₂.
 11. The electrochemical cell of claim 8, wherein said cathode is NaWO₂ Cl₂ or Na₃.5 Ti₂ (PO₄)₃.
 12. The electrochemical cell of claim 8, wherein said organo-disulfide redox polymers are formed by reversible electrochemical dimerization/scission or polymerization/de-polymerization of organo disulfide polymers by the reaction:

    --(S--R--S).sub.n --+2ne.sup.- =nS.sup.-  --R--S.sup.-

wherein R is an aliphatic or aromatic entity and n>50.
 13. The electrochemical cell of claim 12, wherein said organo-disulfide redox polymer is 2,5 dimercapto-1,3,4-thiadiazole.
 14. The electrochemical cell of claim 8, wherein said organo-disulfide/polyaniline composite is a mixture of polyaniline and 2,5 dimercapto-1,3,4-thiadiazole.
 15. An electrochemical cell comprising a non-aqueous electrolyte solvent and an electrolyte additive including an aza-ether based anion receptor compound, wherein said electrolyte solvent is an amorphous polymer electrolyte including a lithium salt dissolved in linear polyethers.
 16. The electrochemical cell of claim 15, wherein said linear polyethers are poly(ethylene oxide) selected from the group consisting of polymer networks, branched polymers and comb-shaped polymers having flexible inorganic backbones.
 17. The electrochemical cell of claim 15, wherein said polymer electrolyte further comprises a plasticizer.
 18. The electrochemical cell of claim 15, wherein said plasticizer is selected from the group consisting of ethylene carbonate, propylene carbonate, and ethylene carbonate with ethylene oxide chains attached to the 4-position.
 19. An electrochemical cell comprising a non-aqueous electrolyte solvent and an electrolyte additive including an aza-ether based anion receptor compound, wherein said electrolyte solvent is a gel electrolyte comprising a solution of lithium salt in a liquid organic solvent, said solution supported by a supporting polymeric matrix.
 20. The electrochemical cell of claim 19, wherein said lithium salt is selected from the group consisting of LiCF₃ SO₃, LiN(CF₃ SO₂)₂, LiCl and LiBr.
 21. The electrochemical cell of claim 19, wherein said supporting polymeric matrix is selected from the group consisting of poly(acrylo nitrile), poly(vinylidene fluoride) and a radiation polymerized acrylic polymer matrix.
 22. The electrochemical cell of claim 19, wherein said liquid organic solvent is a compound selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, dimethyl ether, γ-butyrolactone, 3-methyl-2-oxazolidinone and a mixture thereof.
 23. The electrochemical cell of claim 19, further comprising an electrolyte solute consisting of LiClO₄, LiAsF₆, LiBF₄, LiPF₆ and LiSbF₆, LiCF₃ SO₃, LiN(CF₃ SO₂)₂, LiB(C₆ H₃)₄, LiSO₃ F, LiAlCl₄, LiC(SO₂ CF₃ F)₃ and mixtures thereof.
 24. A method for enhancing the conductivity of an alkali battery non-aqueous liquid electrolyte which comprises adding to said electrolyte a conductivity enhancing amount of an anion receptor compound.
 25. The method of claim 24, wherein said anion receptor compound is a substituted aza-ether bearing an electron withdrawing group.
 26. The method of claim 25, wherein said substituted aza-ether is selected from the group consisting of substituted linear aza-ethers, substituted multi-branched aza-ethers, substituted aza-crown ethers and mixtures thereof.
 27. The method of claim 26, wherein said substituent is selected from the group consisting of CF₃ SO₂, CF₃ CO, CN and SO₂ CN.
 28. A method of making an electrochemical cell having enhanced conductivity, which comprises:providing an alkali metal anode; providing a cathode compatible with said alkali metal anode; and a non-aqueous liquid electrolyte including a conductivity-enhancing amount of an aza-ether based anion receptor compound.
 29. The method of claim 28, wherein said anion receptor compound has at least one electron withdrawing group.
 30. The method of claim 29, wherein said electron withdrawing group is selected from the group consisting of CF₃ SO₂, CF₃ CO, CN and SO₂ CN.
 31. The method of claim 28, wherein said aza-ether based compound is selected from the group consisting of substituted linear aza-ethers, substituted branched aza-ether and substituted crown ethers.
 32. The method of claim 28, wherein said anode is a compound selected from the group consisting of lithium or sodium metal, lithium or sodium alloys, lithium carbon intercalation compounds, lithium graphite intercalation compounds, lithium metal oxide intercalation compounds, and mixtures thereof.
 33. The method of claim 28, wherein said cathode is a compound selected from the group consisting of Li₂.5 V₆ O₁₃, Li₁.2 V₂ O₅, LiCoO₂, LiNiO₂, LiMn₂ O₂, LiMnO₂, Na₂ V₂ O₅, NaCoO₂, NaTaS₂, NaTiS₂, Na₄ Mo₆ S₈, Li₃ NbSe₃, LiTiS₂ and LiMoS₂.
 34. The method of claim 28, further comprising providing an electrolyte solvent selected from the group consisting of tetrahydrofuran, 2-methyl furan, 4-methyldioxolane, 1,3-dioxolane, 1,2-dimethoxyethane, dimethoxymethane, ethylene carbonate, propylene carbonate, γ-butyrolactone, methyl formate, sulfolane, acetonitrile, 3-methyl-2-oxazolidinone, dimethyl carbonate, dimethyl ether and mixtures thereof.
 35. The method of claim 28, further comprising providing an electrolyte solvent selected from the group consisting of polymer electrolytes and gel electrolytes.
 36. The method of claim 28, further comprising providing an electrolyte solute selected from the group consisting of LiClO₄, LiAsF₆, LiBF₄, LiPF₆ and LiSbF₆.
 37. The method of claim 28, further comprising providing an electrolyte solute selected from the group consisting of LiCl, LiBr and LiI. 